Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering or brazing
  • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W99/00—Subject matter not provided for in other groups of this subclass
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
  • B22F1/102—Metallic powder coated with organic material
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W70/00—Package substrates; Interposers; Redistribution layers [RDL]
  • H10W70/01—Manufacture or treatment
  • H10W70/05—Manufacture or treatment of insulating or insulated package substrates, or of interposers, or of redistribution layers
  • H10W70/093—Connecting or disconnecting other interconnections thereto or therefrom, e.g. connecting bond wires or bumps
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W70/00—Package substrates; Interposers; Redistribution layers [RDL]
  • H10W70/60—Insulating or insulated package substrates; Interposers; Redistribution layers
  • H10W70/62—Insulating or insulated package substrates; Interposers; Redistribution layers characterised by their interconnections
  • H10W70/66—Conductive materials thereof
  • H10W70/666—Organic materials or pastes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

• the invention relates generally to coated spheres and methods of making same. More particularly, the invention relates to the method of applying a protective coating to solder alloy spheres by a process of vapor deposition.
• a first method includes mounting the components to a first side of a circuit board. Leads from the components extend through holes formed in the circuit board and are soldered on an opposing side ofthe board.
• a second method includes soldering components on the same side ofthe printed circuit board to which they are mounted. These latter components are said to be "surface-mounted" to circuit boards.
• surface mounting electronic components to circuit boards and other electronic substrates is a desirable method in that the method may be used to fabricate very small circuit structures.
• surface mounting lends itself well to process automation.
• surface mountable microelectronic devices are bonded to a substrate by a solder reflow process.
• One type of surface mountable device commonly referred to as a "flip chip,” comprises an integrated circuit device having numerous connecting leads that are attached to pads mounted on the underside of the device.
• solder spheres are formed prior to the reflow process by any of various prior art processes which include deposition through a mask, electroplating, pick-and-place, evaporation, sputtering, and screen printing.
• the chip is mounted to the circuit board or other electronic substrate by (a) placing it in contact with the board such that the solder spheres become sandwiched between the pads on the board and the corresponding pads on the chip forming an assembly; (b) heating the assembly to a point at which the solder reflows: and (c) cooling the assembly. Upon cooling, the solder hardens, thereby mounting the flip chip to the surface of the circuit board.
• Tolerances in devices using flip chip technology are critical, as the spacing between individual devices as well as the spacing between the chip and the circuit board is typically very small. For example, spacing of such chips from the surface of the board is typically in the range of 0.5 to 3.0 mil and is expected to approach micron spacing in the near future.
• solder spheres of precisely controlled diameter and unblemished surface condition between circuit pads. Solder spheres are then heated above the liquidus temperature ofthe solder alloy, thereby melting the solder spheres, which wets and flows onto both contact pads, creating a mechanical and an electrical contact.
• solder alloys consist of relatively soft base metals such as aluminum or copper that can be easily damaged by mechanical agitation. Such damage may result in, for example, the formation of surface flat cracks and crevices; spalling off portions ofthe spheres as particles or flakes; loss of the bright reflective sphere surface; increased sphere electrical contact and bulk resistivity; and an exacerbation of base metal oxidation at the sphere surface.
• Damage to the solder sphere surface may produce a range of consequences. For example, automated vision system assembly hardware will not be able to distinguish a solder sphere from the background if the sphere reflectivity has been diminished. Additionally, physical surface damage will hinder the ability of most automated BGA assembly hardware to pick and place individual spheres. Furthermore, the presence of extraneous particles on the solder spheres may impair the mechanical function of the BGA assembly hardware and cause low resistivity or electrical shorts between contact pads on the microelectronic package, and impact electrical performance once the BGA joints have been created. Importantly, excessive oxide present on the solder sphere surface can impair proper wetting and flow of solder spheres into contact pads as necessary to form an adequate mechanical joint and electrical connection. In an effort to protect solder sphere surfaces from oxidation, the production of solder spheres coated with low melting point materials such as solder or flux has previously been disclosed in U.S. Patent Nos. 5,872,400 and 5.736,074.
• the present invention provides a rapid and efficient method of coating solder alloy spheres to prevent mechanical surface damage and surface oxidation of alloy metals.
• the invention provides a method for applying a chemical coating to surfaces of solder alloy spheres to ameliorate or eliminate mechanical damage due to contact and collision ofthe solder alloy spheres with other solder spheres and side walls of containers used for storing and transporting the solder alloy spheres.
• chemically coating surfaces ofthe solder alloy spheres ameliorates or eliminates oxidation of metal alloys comprising surfaces of the solder spheres.
• the method ofthe invention includes the step of providing a first vapor-tight chamber into which a coating solution, formulated as described herein and comprising a volatile organic solvent and at least one solute, such as a low viscosity organic material and a surfactant.
• the method further includes the step of providing a second chamber containing a plurality of solder spheres and immersing the second chamber into the solution contained in the first vapor-tight chamber.
• the solder spheres are in fluid communication with the coating solution by a plurality of apertures or perforations formed in the second chamber.
• the solder spheres are immersed in the coating solution for a desired predetermined residence time.
• the second chamber with the solder spheres contained therein is removed from the first vapor-tight chamber and placed in a second vapor- tight chamber.
• the second vapor-tight chamber is heated to a temperature above a boiling point of the solvent used in the coating solution by a heating device in order to vaporize any solvent remaining that did not adhere to surfaces of the solder spheres.
• vaporization of excess solvent may be accomplished by decreasing a pressure in the second vapor-tight chamber.
• the second chamber with the solder spheres contained therein is removed.
• the temperature of the second vapor-tight chamber may be controlled by a thermal sensor.
• the second vapor-tight chamber may be additionally equipped with a condenser to condense excess solvent vapors and a collection device for collecting the condensed solvent vapors for reuse.
• the coating solution may include the volatile organic solvent selected from the group consisting of acetone, isopropyl alcohol, denatured ethanol, n-propyl bromide, trichloroethylene, Genesolve 2000TM, EnsolvTM. Asahi AK-225TM and Vaporedge 1000TM.
• the coating solution contains the low viscosity organic material which may be selected from the group consisting of paraffin oil, mineral oil, isostearic acid, polyolefin oil, adipic acid, silicone oil, petroleum oil and tin, and any combination thereof.
• the low viscosity organic material is present at a concentration of from about 0.05 percent by weight to 5.0 percent by weight (wt.%).
• the surfactant of the coating solution may be selected from the group consisting of simethicone, cyclomethicone, decamethylcyclopentasiloxane, and any combination thereof.
• the surfactant is present at a concentration of from about 0.01 wt. % to about 1.0 wt. %.
• the coating solution may further include a solvent-soluble ultraviolet UV fluorescent dye known to those skilled in the art as a fluor.
• a coating solution containing a fluor leaves a UV fluorescent deposit on surfaces ofthe solder spheres that assists to optically locate the solder spheres.
• the UV fluorescent dye is present at a concentration of from about 0.01 to about 0.1 wt. %.
• the coating solution may also include a solvent-soluble, polar or non-polar solder flux that minimizes or eliminates the need for a separate deposition of liquid flux or flux paste onto surfaces of the solder spheres during the reflow phase of surface mounting.
• the solder flux is present at a concentration of from about 05 to about 1.0 wt. %.
• Fig. 1 is a flow diagram of a method of coating solid spheres in accordance with the invention.
• Embodiments of the present invention described below provide a method for coating solder alloy spheres by a vapor deposition process. More particularly, the method protectively coats solder alloy spheres and ameliorates or eliminates mechanical damage to and oxidation of solder sphere surfaces. Those skilled in the art will appreciate, however, that embodiments in accordance with the invention are not limited to coating solder alloy spheres, but rather, may be used in other applications that require coating metallic objects to reduce or prevent mechanical and chemical surface damage.
• the spheres ofthe invention can be any suitable material useful as a solder sphere.
• the solder spheres may be constructed of such materials as, although not limited to, aluminum, lead, tin, copper, gold, nickel, bismuth, gallium, silver, cobalt, cadmium, antimony, silicon, germanium, tellurium, indium and mixtures, solutions or alloys of two or more of such metals.
• the method of protectively coating the solder spheres includes providing an immersible container with a plurality of apertures or perforations in which the solder spheres will be contained 100 during the vapor deposition process.
• the plurality of apertures or perforations allows a sufficient volume of solvent to contact the solder spheres contained therein.
• the immersible, perforated container is constructed of material that does not react with volatile organic solvents, coating solutes, or low-viscosity organic coating materials used in accordance with the invention. Furthermore, the immersible container is stable at the elevated temperatures employed in the vapor deposition process.
• the coating process includes preparing a coating solution that contains a solvent and coating solutes as described herein 1 10.
• the solvent may include a volatile organic solvent that is inert to the components comprising the immersible container, such as, but not limited to, acetone, isopropyl alcohol, denatured ethanol. n-propyl bromide, trichloroethylene, Genesolve 2000TM, EnsolvTM, Asahi AK-225TM and Vaporedge 1000TM.
• solvent used in the coating process does not leave a residue on surfaces of the solder spheres upon proper evaporation.
• the coating solution includes a low viscosity organic material (LVOM) and a surfactant.
• the LVOM is present in solution at a concentration of from about 0.05 to about 5 percent by weight (wt. %). More preferably, the LVOM may be present in solution from about 0.5 to about 2 wt. %, and most preferably from about 0.1 to about 1.0 wt. %.
• the LVOM that may be used in the coating solution include, but are not limited to, paraffin oil, mineral oil, isostearic acid, polyolefin oil, adipic acid, silicone oil, petroleum oil and tin stearate.
• the LVOM may be present as a mixture of one or more types of such materials.
• the surfactant is present in solution at a concentration of from about 0.01 to about 1.0 wt. %. More preferably, the surfactant may be present in solution at a concentration of from 0.05 to about 0.75 wt. %, and most preferably, at a concentration of from about 0.1 to about 0.5 wt. %.
• Suitable surfactants for use in the coating process include, but are not limited to, simethicone, cyclomethicone, decamethylcyclopentasiloxane, and any combination thereof.
• the coating solution may include ultraviolet (UV) fluorescent dyes, known in the art as fluors, which are soluble in the coating solution solvent.
• UV fluorescent ultraviolet
• fluors which are soluble in the coating solution solvent.
• Use of fluors in the coating solution described herein leaves a UV fluorescent deposit on surfaces of the solder spheres.
• the UV fluorescent deposit aids in location ofthe solder spheres on a substrate with an optical character recognition system or other vision system for optically locating the solder spheres.
• fluors of different colors may be used to represent and identify different solder sphere alloy compositions by fluorescing in different colors upon ultraviolet stimulation. Fluors are preferably present in the coating solution at a concentration of from about 0.01 to about 0.1 wt. %.
• the coating solution may further include polar and non- polar fluxes which are soluble in the coating solution solvent.
• the addition of flux to the coating solution helps to assist the processing of the solder spheres during the reflow process of surface mounting. A flux deposit remains on surfaces ofthe solder spheres after excess solvent that does not adhere to surfaces ofthe solder spheres is removed.
• the flux component ofthe coating solution ameliorates or eliminates the need for the separation addition of flux liquid or flux paste during the reflow process.
• the flux may be present in the coating solution in a concentration of from about 0.5 to about 1.0 wt. %.
• the coating process further includes placing the coating solution, as described herein, in a first vapor-tight chamber 1 15.
• the coating process then includes immersing the perforated container with the solder spheres contained therein in the solution contained in the first vapor-time container for a desired predetermined residence time 120.
• a preferred residence time is from about 30 seconds to about 12 hours. More preferably, the residence time may be from about 30 seconds to about 10, 8, 6, 4, or 2 hours and most preferably, the residence time may be from about 1 minute to one hour.
• the perforated container is removed from the first vapor-tight chamber 140 and placed into a second vapor-tight chamber 150.
• the second vapor-tight chamber is fitted with a heating element capable of heating the chamber.
• the second vapor-tight chamber may be additionally fitted with a device for monitoring the temperature of the second vapor-tight chamber, such as, but not limited to, a thermal electrode.
• the second vapor-tight chamber is heated to a temperature above the boiling point ofthe solvent used in the coating solution in order to remove by vaporization excess coating solution solvent.
• the second chamber is heated to a temperature of from about 54 to about 121 °C.
• the second vapor-tight chamber is heated for a period of from 5 minutes to 10 hours.
• the second vapor-tight chamber may be heated more preferably from about 10 minutes to about 5 hours, and most preferably from about 15 minutes to about 2 hours.
• excess solvent that has not sufficiently adhered to surfaces of solder spheres is removed from surface coatings by vaporization 170. Vaporization yields the solder spheres protectively coated with the solutes present in the coating solution.
• the perforated container is removed from the second vapor-tight chamber 180 and the solder spheres may be immediately used or stored for later use.
• the excess coating solution solvent that has not sufficiently adhered to the solder spheres may be removed by from the surface coatings by vaporization achieved by decreasing the internal pressure of the second vapor-tight chamber.
• the second vapor-tight chamber may be further fitted with a device for condensing the solvent vapors that evolve from heating the surface coatings ofthe solder spheres.
• the second vapor-tight chamber may be additionally equipped with a cold plate or other condensing device to condense circulating solvent vapors, and a collecting device to thereafter collect the condensed solvent vapors for reuse.
• the protectively coated solder spheres produced in accordance with the method ofthe invention may be used in many electronic applications.
• the chemically coated solder spheres may be used in interconnect arrays, solder pastes, Z-axis conduction adhesives, etc.
• a coated solder sphere may be ejected or printed onto a substrate and stored without damage to the solder for reflow at a future time.
• the coating of the solder spheres maintains an oxide-free surface ofthe solder sphere and provides surface activation for reflow ofthe solder sphere when the interconnect joint is formed.
• the chemically coated solder spheres may also be used for flip-chip, ball grid array and fine pitch surface mount applications.
• the chemically coated solder spheres may also be used to produce solder pastes or the like, or may be directed onto wettable metal pads of electronic devices or the like.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)
• Wire Bonding (AREA)

Applications Claiming Priority (5)

Publications (1)

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Family Cites Families (2)

• 2000
  • 2000-06-01 KR KR1020017015481A patent/KR100725075B1/ko not_active Expired - Fee Related
  • 2000-06-01 EP EP00938067A patent/EP1232524A1/en not_active Withdrawn
  • 2000-06-01 JP JP2001500332A patent/JP2004500700A/ja active Pending
  • 2000-06-01 AU AU53156/00A patent/AU5315600A/en not_active Abandoned

Non-Patent Citations (1)

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